Report type Deliverable Work Group WP1...MOSARIM No.248231 28.06.2010 File: MOSARIM_Deliverable_1.5_V1.6.doc 4/70 3.1.22 PREF22 – Radar device and methods for suppression of disturbance

Contract no.: 248231

MOre Safety for All by Radar Interference Mitigation

D1.5 – Study on the state-of-the-art interference mitigation techniques

Report type Deliverable

Work Group WP1

Dissemination level Public

Version number Version 1.6

Date 28.06.2010

Lead Partner Robert Bosch GmbH

Project Coordinator Dr. Martin Kunert

Robert Bosch GmbH Daimler Strasse 6

71229 Leonberg Phone +49 (0)711 811 37468

[email protected]

copyright 2010

the MOSARIM Consortium

MOSARIM No.248231 28.06.2010

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Authors

Name Company

Martin Kunert Robert Bosch GmbH (RB)

Frantz Bodereau Autocruise S.A.S (AC)

Markus Goppelt Daimler AG (DAI)

Christoph Fischer Daimler AG (DAI)

Andreas John Hella KGaA Hueck & Co. (HKG)

Thomas Wixforth Hella KGaA Hueck & Co. (HKG)

Alicja Ossowska Valeo Schalter und Sensoren (VIC)

Tom Schipper Karlsruher Institut für Technologie (KITU)

Robert Pietsch Continental AG (ADC)

Revision chart and history log

Version Date Reason

0.1 30.04.2010 Initial version by Martin Kunert

0.11 14.05.2010 Inputs from AC

0.2 14.05.2010 Inputs from DAI and HKG

0.3 19.05.2010 Consolidation of all inputs (M. Kunert)

0.4 21.05.2010 Inputs from VIC and RB

0.5 26.05.2010 Input from HKG

0.6 27.05.2010 Input from ADC

0.65 27.05.2010 Input from KIT-U

0.7 31.05.2010 Input from KIT-U

0.8 10.06.2010 Input from HKG on PREF06,CREF11,CREF12

0.9 10.06.2010 Input from AC on CREF17, CREF18, CREF20

1.0 11.06.2010 Input from ADC on CREF23, CREF24

1.1 14.06.2010 Version for Peer Review

1.2 17.06.2010 Reviewed by HKG

1.3 18.06.2010 Consolidated peer reviews

1.3a 22.06.2010 Inputs from steering group by M. Kunert

1.4 23.06.2010 Reviewed by HKG

1.5 28.06.2010 Reviewed by VIC

1.6 28.06.2010 Final version for submission

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Table of content

Authors..................................................................................................................................... 2 Revision chart and history log........................................................................................... 2 1 Introduction ........................................................................................................................ 6

2 Basic interference mitigation techniques ........................................................................... 6

2.1 Interference mitigation in the polarization domain .................................................... 6

2.2 Interference mitigation in the time domain ................................................................ 8

2.3 Interference mitigation in the frequency domain ....................................................... 8

2.4 Interference mitigation in the coding domain ............................................................ 9

2.4.1 Variations on the CDMA approach.................................................................... 9

2.5 Interference mitigation in the space domain ............................................................ 10

2.6 Interference mitigation by strategic approaches....................................................... 10

3 Survey database overview................................................................................................ 11

3.1 Patent survey database ............................................................................................. 14

3.1.1 PREF01 – Method of preventing interference between radars and radar system

having interference preventing function .......................................................................... 14

3.1.2 PREF02 – Radar sensor having a CFAR detector............................................ 15

3.1.3 PREF03 – Radar apparatus and radar system for a vehicle ............................. 15

3.1.4 PREF04 – Automotive radar with composite multi-slope FM chirp waveform

16

3.1.5 PREF05 – Fourier-transform-based adaptive radio interference mitigation .... 17

3.1.6 PREF06 – Doppler Radar................................................................................. 17

3.1.7 PREF07 – Frequency-phase coding device...................................................... 18

3.1.8 PREF08 – System and method for reducing a radar interference signal ......... 18

3.1.9 PREF09 – Pulse Doppler radar interference reduction method for vehicle anti-

collision or building security system................................................................................ 21

3.1.10 PREF10 – Interference determination method and FMCW Radar using the

same 22

3.1.11 PREF11 – Interference Avoidance System for Vehicular Radar System ........ 23

3.1.12 PREF12 – Vehicular distance-warning radar................................................... 26

3.1.13 PREF13 – Radar system for detecting surroundings with compensation of

interfering signals ............................................................................................................. 26

3.1.14 PREF14 – Method for the suppression of disturbances in systems for detecting

objects 27

3.1.15 PREF15 – Automotive radar system with anti-interference means ................. 28

3.1.16 PREF16 – Interference rejection method for an automotive radar CW/ICC

system 29

3.1.17 PREF17 – Procedure for the elimination of interference in a radar unit of the

FMCW type...................................................................................................................... 30

3.1.18 PREF18 – FMCW Radar Device and Method for Detecting Interference ...... 32

3.1.19 PREF19 – Adding error correction and coding to a radar system ................... 34

3.1.20 PREF20 – Method for operation of a radar device .......................................... 35

3.1.21 PREF21 – Bridge detecting and false warning suppressing method for motor

vehicle, involves suppressing controller of speed controlling system changing driving

conditions of vehicle, when identified objects are classified to pre-set object class ....... 36

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3.1.22 PREF22 – Radar device and methods for suppression of disturbance of a radar

device 36

3.2 Conference paper database....................................................................................... 38

3.2.1 CREF01 – Reduction of Interference in Automotive Radars using Multiscale

Wavelet Transform........................................................................................................... 38

3.2.2 CREF02 – Reduction of Interference in Microwave Automotive Radars ....... 38

3.2.3 CREF03 – Research on Key Technologies for Collision Avoidance

Automotive Radar ............................................................................................................ 39

3.2.4 CREF04 – SS-FH signals used for very low interference in vehicular cruising

control systems................................................................................................................. 40

3.2.5 CREF05 – Time-Varying Interference Suppression in Communication Systems

Using Time-Frequency Signal Transforms ...................................................................... 41

3.2.6 CREF06 – Wavelet domain communication system (WDCS) interference

avoidance capability: analytic, modelling and simulation results.................................... 41

3.2.7 CREF07 – Novel pulse-sequences design enables multi-user collision-

avoidance vehicular radar................................................................................................. 42

3.2.8 CREF08 – A Novel Transmit signal Based on High Range- Resolution

Concept for FLAR or AICC System Applications........................................................... 43

3.2.9 CREF09 – Agile Digital Detector for RFI Mitigation ..................................... 44

3.2.10 CREF10 – Adaptive Reduced-Rank Interference Suppression Based on the

Multistage Wiener Filter .................................................................................................. 44

3.2.11 CREF11 – Airborne Radar Interference Suppression Using Adaptive Three-

Dimension Techniques ..................................................................................................... 45

3.2.12 CREF12 – Combining raised cosine windowing and per tone equalization for

RFI mitigation in DMT receivers..................................................................................... 45

3.2.13 CREF13 – OFDM as a possible modulation technique for multimedia

applications in the range of mm waves ............................................................................ 46

3.2.14 CREF14 – Listen before talk technique ........................................................... 46

3.2.15 CREF15 – Detect and avoid technology .......................................................... 47

3.2.16 CREF16 – A Real Time Signal Processing for an Anti-collision Road Radar

System 48

3.2.17 CREF17 – Hardware/Software Exploration for an Anti-collision Radar System

48

3.2.18 CREF18 – Conceptual design of a dual-use radar/communi-cation system

based on OFDM ............................................................................................................... 49

3.2.19 CREF19 – Mutual Interference of Millimeter-Wave Radar Systems .............. 49

3.2.20 CREF20 – SiGe Circuits for Spread Spectrum Automotive Radar ................. 50

3.2.21 CREF21 – Design and Demonstration of an Interference Suppressing

Microwave Radiometer .................................................................................................... 50

4 Summary and Outlook ..................................................................................................... 52

5 Annex A – Overview of different coding techniques ...................................................... 53

5.1 Interference mitigation considered as a multiple access situation ........................... 53

5.2 Desired properties for a multiple access automotive radar ...................................... 53

5.3 Multiple access approaches ...................................................................................... 54

5.3.1 Overview of multiple access approaches for narrowband signal ..................... 54

5.3.2 Applicability of the FDMA approach: ............................................................. 55

5.3.3 Illustrative applications of CDMA................................................................... 56

5.4 Applications of multiple access telecommunication techniques to automotive radar

57

5.4.1 Applications of DS-CDMA to automotive radar ............................................. 57

5.4.2 Applications of FHSS to automotive radar ...................................................... 59

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5.4.3 Applications of Ultra-Wide Band (UWB) to automotive radar ....................... 60

5.4.4 Applications of MC-CDMA to automotive radar ............................................ 61

5.5 Conclusions .............................................................................................................. 62

5.5.1 Future steps ...................................................................................................... 63

6 Bibliography..................................................................................................................... 64

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1 Introduction

The topic of possible interference is inherent to all wireless applications sharing the same or

an overlapping frequency range. Also automotive radars are exposed to various emissions

from other frequency users such as automotive radars in others cars at low distance, other

radars roadside or near roads such as speed radars, radars for surveillance purposes e.g. such

as surveillance of rail-road crossings or surveillance of buildings. The characteristics of these

transmitters is within the limits of ETSI standards or country specific standards in most cases,

may however be much higher in some cases especially in cases of governmental use.

Because of that inherence, already in the past techniques to mitigate interference between

different or even same devices were investigated. Obvious techniques to reduce interference

risk are:

• transmitters use low power or a low duty cycle, a narrow bandwidth and a narrow beam width

• receivers have a low bandwidth and a narrow beam width.

But these properties are normally in contradiction with requirements for optimum application

performance, so that more sophisticated mitigation techniques are desired.

Section 2 gives a summary of such more sophisticated state-of-the-art techniques and section

3 a short description of respective references that were found in a patent and conference paper

survey.

The established patent and paper database regarding interference mitigation techniques for

radio-location applications will be used within the MOSARIM research project as a starting

point to investigate and elaborate further mitigation techniques for automotive radar

applications.

2 Basic interference mitigation techniques Based on the results of the patent and conference paper survey conducted, the different

mitigation techniques are classified in six different basic techniques that are described in their

principle operation modes in the following sections. The different basic techniques can also

be combined to further reduce the probability of a radar-malfunction.

2.1 Interference mitigation in the polarization domain

Electromagnetic waves exhibit polarization that is a property describing the orientation of

their oscillations. Depending on the phase and amplitude of the complex electromagnetic

vector one can differentiate between the following three polarization states:

a) linear polarization: The two orthogonal components of the electromagnetic vector are

in phase with same amplitude

b) circular polarization: The two orthogonal components of the electromagnetic vector

have the same amplitude and are exactly 90 degrees out of phase

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c) elliptical polarization: The two orthogonal components of the electromagnetic vector are

not in phase and have either not the same amplitude or are not

exactly 90 degrees out of phase

These three polarization states are

graphically shown in the right Figure.

For circular and elliptical

polarization the rotation of the

electromagnetic field vector depends

on the relationship between the two

phases and turns either clockwise

(left hand circular) or counter-

clockwise (right hand circular).

Depending on what kind of

polarization is used the wave

generation principle and the used

antenna types may vary. Almost all

automotive radar devices use the

linear polarization. The orientation

of the electric field vector, however,

differs from radar device to radar

device and is often either

horizontally or vertically oriented.

While for circular and elliptical polarization a decoupling or interference mitigation effect by

choosing a specific circular or elliptical polarization is not possible, this can be well done with

linear polarization. (Remark: Reflection or scattering on objects may alter the polarization

direction of linear polarized electromagnetic waves).

The decoupling effect that can be attained by changing the polarization direction of a dish

antenna is shown in Figure 2.1.1.

Figure 2.1.1: Co- and Cross polar pattern of a dish antenna

Attenuation of antenna pattern w.r.t. main beam deviation

0

5

10

15

20

25

30

35

40

3,5 3

2,5 2

1,5 1

0,5 0

0,5 1

1,5 2

2,5 3

3,5

Deviation from main beam in °

Att

en

uati

on

in d

B

Cross Co

0

5

10

15

20

25

30

35

40

3,5 3

2,5 2

1,5 1

0,5 0

0,5 1

1,5 2

2,5 3

3,5

Att

en

uati

on

in d

B

Cross-pattern Co-pattern

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It can be concluded that by using 90 degree between the polarization direction of the interferer

antenna and the victim antenna a decoupling of typically more than 20 dB can be achieved.

The decoupling effect depends on the specific antenna parameters.

Remark: Only the direct LOS (Line of Sight) propagation is taken into account and multipath

reflection or reflection at nearby obstacles are neglected. Reflections on ground surface and

other obstacles may turn the polarization of the transmitted electromagnetic wave. So the true

cross-polarization interference mitigation effect may be reduced in the presence of obstacle

reflection.

Conclusion:

By using cross-polarized orientation between the victim and interferer antenna the

interference effects can be mitigated in the order of 20 dB ±10 dB.

2.2 Interference mitigation in the time domain

To measure the distance to target objects, radar sensors usually apply a time domain

modulation of the radar transmit frequency. With the same time dependency, normally the

centre frequency of the receiver bandwidth is modulated. Interference now occurs if an

interferer transmission frequency accidentally hits the victim receiver bandwidth.

To mitigate interference effects, the following time domain approaches are feasible:

• Use an as low as possible transmit duty cycle in order to reduce the probability of hitting a victim receiver bandwidth

• Use an as short as possible receiver measuring time in order to reduce the probability of being hit by an interferer transmitter

• Use a random timing of the used time domain modulation of transmit frequency (for example vary a pause length before a next FMCW chirp starts or vary a FMCW slope)

in order to avoid periodic interferences

2.3 Interference mitigation in the frequency domain

Interference mitigation techniques in the frequency domain consist of measures which avoid

that other radars transmit in the reception bandwidth of a given radar. To achieve this, the

reception bandwidth of the victim radar and/or the transmission bandwidths of the interfering

radars need to be shifted in order to separate them in the frequency domain. That is achieved

by introducing sub-bands as shown in Fig. 2.3.1. This makes sense when all radars have the

same reception bandwidth that covers only parts of the designated frequency range defined by

the frequency authorities.

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f

t

f

t

f

t

f

t

Fig. 2.3.1: Division of a frequency band into five sub-bands. The shown three radars have the

same transmission and reception bandwidth

2.4 Interference mitigation in the coding domain

For the study of work package 1.5 coding techniques will be considered mostly in their role as

enablers for multiple access to a common resource. Specifically, in automotive radar systems

(Adaptive Cruise Control or Short Range Radars) the shared resource is the frequency band

allocated for radar operation. In this context, coding refers to a technique using a device

specific code for the radar waveform modulation. The same code is used in the demodulation

stage, allowing each user (device) to recover the measurement data corresponding to its code.

Codes for multiple access must satisfy to orthogonality relations, in order to minimize the

crosstalk between different users.

The description of coding above is more specific than the definition used in the field of

telecommunications, where coding refers to various techniques used to adapt the information

rate to the channel used for transmission. In this context the adaption does not necessarily

focus on perturbations by other users, but also on improvements to bit error rates in noisy

channel situations. Nevertheless, coding techniques used in telecommunications systems can

serve as a source of inspiration for multiple access radar systems. This field is generally

referred to as CDMA (for Code Division Multiple Access). [OR98].

2.4.1 Variations on the CDMA approach

The CDMA approach can have multiple expressions, as illustrated schematically in Fig.

2.4.1.1.

Figure 2.4.1.1 - Schematic representation of 3 approaches to CDMA Excerpt from [OR98]

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- Direct-sequence (DS-) CDMA implies a direct coding of the bit stream transmitted by the emitter. This technique is used is used for example in GPS and Galileo navigation

devices, as well in Wi-Fi systems (IEEE802.11b). It is also referred to as DSSS

(Direct Sequence Spread Spectrum).

- In frequency-hopping spread spectrum (FHSS), the code is used to determine the width of frequency jumps which are performed at a constant repetition rate. This

technique requires frequency agile modulation and demodulation. It is used for

example in the Bluetooth protocol.

- In time-hopping spread spectrum, the amplitude of the transmitted signal is modulated in time intervals given by the code.

- In multiple-carrier (MC-) CDMA (not illustrated), each user is allowed to transmit simultaneously on multiple subcarriers, the frequency spacing between the subcarriers

being given by the code. The orthogonal frequency division multiple access

(OFDMA) approach can be considered as a specific case of MC-CDMA. It is used in

the IEEE802.16 WiMax standard.

In Annex A a more detailed study and overview of the different coding techniques is provided.

2.5 Interference mitigation in the space domain

For applications where a certain azimuth or elevation range is covered, a mechanically or

electronically scanned beam can be used to reduce interference risk. Furthermore, interference

risk can be mitigated by choosing the scanned azimuth or elevation range adaptive to the

current environment to be just as small as necessary for the current application.

2.6 Interference mitigation by strategic approaches

Using additional hardware and/or software, mitigation can be achieved in the following more

sophisticated ways:

Communicate and avoid With the availability of inter-vehicle communication, timing

and/or frequency bands could be negotiated to avoid that radars

transmit at the same time in the reception bandwidth of other

radars.

Detect and avoid Some ways of interference can be detected in the time domain

(see for example peak in Fig. 2.6.1) or in the frequency domain

and the used timing or frequency bands changed (see example

in Fig. 2.6.2). In the space domain, interference from a certain

azimuth angle can be avoided by leaving out just that azimuth

angle during a scan.

Detect and repair As before, but after interference is detected, in some cases it is

possible to repair the disturbance or lower it by adapting

detector thresholds. In Fig. 2.6.1 for example, the peak can be

eliminated using a Median filter.

Detect and omit As before, but after interference is detected, the interfered

measurement results are not used for further processing.

Listen before talk Only start to transmit if no other device is sensed to be active

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Fig. 2.6.1: Example of received time domain signal with single peak-shaped interference

f

t

f

t

Fig. 2.6.2: Three radars share a frequency band while the orange one chose its frequency

range after interference was detected with other radars.

3 Survey database overview

In this chapter, the patents and conference papers that are collected in an interference

mitigation technique database on the MOSARIM web-server are described in a short form to

provide the reader with the basic idea and principle of the mitigation effects. Based on this

information the reader can decide whether to read the complete document in the database or to

skip it.

An overview of the patents is given in Table 3.1 and of the conference papers in Table 3.2. .

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Section Short

form

Title Basic

technique(s)

Expected

interference

mitigation

effect 3.1.1 PREF01 Method of preventing interference

between radars and radar system having

interference preventing function

Communicate and

avoid (time

domain)

high

3.1.2 PREF02 Radar sensor having a CFAR detector Time domain high

3.1.3 PREF03 Radar apparatus and radar system for a

vehicle

Detect and avoid

(various domains)

depends

3.1.4 PREF04 Automotive radar with composite multi-

slope FM chirp waveform

Frequency domain,

time domain

t.b.d.

3.1.5 PREF05 Fourier-transform-based radio

interference mitigation

n/a low (~20 dB)

3.1.6 PREF06 Doppler radar Detect and avoid

(frequency domain)

t.b.d.

3.1.7 PREF07 Frequency-phase coding device Coding domain t.b.d.

3.1.8 PREF08 System and method for reducing a radar

interference signal

Detect and repair

(time domain)

medium (~40 dB)

3.1.9 PREF09 Pulse Doppler radar interference

reduction method for vehicle anti-

collision or building security system

Coding domain low (~15 dB)

3.1.10 PREF10 Interference determination method and

FMCW radar using the same

Detect and repair

(time domain)

t.b.d.

3.1.11 PREF11 Interference avoidance system for

vehicular radar system

Detect and avoid

(frequency domain)

t.b.d.

3.1.12 PREF12 Vehicular distance-warning radar Polarization domain low (10 to 30 dB)

3.1.13 PREF13 Radar system for detecting surroundings

with compensation of interfering signals

Time and frequency

domain

low (~20 dB)

3.1.14 PREF14 Method for the suppression of

disturbances in systems for detecting

objects

Time domain low (~20 dB)

3.1.15 PREF15 Automotive radar system with anti-

interference means

Detect and avoid,

communicate and

avoid (frequency

domain)

high

3.1.16 PREF16 Interference rejection method for an

automotive radar CW/ICC system

Detect and repair

(time domain)

high

3.1.17 PREF17 Procedure for the elimination of

interference in a radar unit of the FMCW

type

Detect and repair

(time domain)

high

3.1.18 PREF18 FMCW radar device and method for

detecting interference

Detect and avoid

(polarization and

frequency domain)

t.b.d.

3.1.19 PREF19 Adding error correction and coding to a

radar system

Coding domain depends

3.1.20 PREF20 Method for operation of a radar device Detect and avoid

(frequency domain)

high

3.1.21 PREF21 Bridge detecting and false alarm

suppressing method for motor vehicle,

involves …

Coding domain medium

3.1.22 PREF22 Radar device and methods for suppression

of disturbance of a radar device

Time domain low (~10 dB)

Table 3.1: Patent reference list overview

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Section Short

form

Title Basic

techniques

Expected

interference

mitigation

effect 3.2.1 CREF01 Reduction of Interference in automotive

radars using multiscale wavelet

transform

Detect and omit

(time domain)

t.b.d.

3.2.2 CREF02 Reduction of interference in microwave

automotive radars

Coding domain ca. 5dB

3.2.3 CREF03 Research on key technologies for

collision avoidance automotive radar

Frequency domain

and time domain

t.b.d.

3.2.4 CREF04 SS-FH signals used for very low

interference in vehicular cruising

control systems

Frequency domain

and coding domain

t.b.d.

3.2.5 CREF05 Time-varying interference suppression

in communication systems using time-

frequency signal transforms

Detect and repair

(frequency domain)

t.b.d.

3.2.6 CREF06 Wavelet-domain communication

system (WDCS) interference avoidance

capability: analytic, modelling and

simulations results

Time domain and

frequency domain

6 – 12dB

3.2.7 CREF07 Novel pulse-sequences design enables

multi-user collision avoidance vehicular

radar

Time domain ca. 10dB

3.2.8 CREF08 A novel transmit signal based on high

range resolution concept for FLAR or

AICC system applications

Coding domain Depends on code

length

3.2.9 CREF09 Agile digital detector for RFI mitigation Only interference

detection

(frequency domain)

t.b.d.

3.2.10 CREF10 Adaptive reduced-rank interference

suppression based on multi-stage

Wiener filter

Coding domain t.b.d.

3.2.11 CREF11 Airborne radar interference suppression

using adaptive three-dimension

technique

Space and time

domain

t.b.d.

3.2.12 CREF12 Combining raised cosine windowing

and per tone equalisation for RFI

mitigation in DMT receivers

Frequency domain t.b.d.

3.2.13 CREF13 OFDM as a possible modulation

technique for multimedia applications

in the range of mm waves

Coding domain ca. 11dB for

impulse noise

3.2.14 CREF14 Listen before talk technique Listen before talk Depends on sensor

density

3.2.15 CREF15 Detect and avoid technology Detect and avoid

(frequency domain)

Depends on

available bandwidth

3.2.16 CREF16 A real time signal processing for an

anti-collision road radar system


3.2.17 CREF17 Hardware/software exploration for an

anti-collision radar system

Coding domain 5 – 10dB

3.2.18 CREF18 Conceptual design of a dual-use

radar/communication system based on

OFDM


3.2.19 CREF19 Mutual interference of millimeter-wave

radar systems

Time domain and

space domain

10 – 30dB

3.2.20 CREF20 SiGe circuits for spread spectrum Coding domain t.b.d.

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Section Short

form

Title Basic

techniques

Expected

interference

mitigation

effect automotive radar

3.2.21 CREF21 Design and demonstration of an

interference suppressing microwave

radiometer

Detect and repair

(time domain,

frequency domain)

Dependent on

observing time

Table 3.2: Conference paper reference list overview

3.1 Patent survey database

3.1.1 PREF01 – Method of preventing interference between radars and radar system having interference preventing function

Abstract:

In this patent the inventor proposes to use time multiplexing for two or more radars mounted

on an automotive vehicle for detecting object. The first radar is detecting object in front of the

vehicle and the second radar is detecting object behind the vehicle or both radars are

positioned close to each other. Proposed is to choose the transmission times for both radars

X1 and X2 with cycle transmission periods T1 and T2 to satisfy the formula:

K·T2+X2+X1≤T1≤(K+1) ·T2-X2-X1, with T1>T2>X1+X2 and K a positive integer. The

sensors are synchronized with transmission times and duration of the transmitted signals. For

two vehicles, in which the periods T1 and T2 and transmission times X1 and X2 are set to

satisfy the above formula, the interference between the two radars on different vehicles

according does not occur continuously more than two times. A single interference is detected

and replaced with an estimation based on a history of previous received data. The invention

prevents the interference between radars without using additional devices in radar system.

Patent reference in Bibliography PREF01

Restriction to a specific radar type Radar system with period T1, T2, and transmission times X1, X2

Implementation effort low

Side-effect with other methods Nothing expected

Mitigation effect on TX path yes (time domain)

Mitigation effect on RX path yes (detection, estimation)

Computational effort low

Interference mitigation category Communicate and avoid (time domain)

Harmonization needed yes

MOSARIM relevant Yes, but not applicable in scenarios with high density of traffic and multiple radar transmitters/receivers

Range of mitigation effect For sensor on single vehicle interference can be completely eliminated

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3.1.2 PREF02 – Radar sensor having a CFAR detector

Abstract: In this patent the inventor proposes to operate radar sensor with a randomized pulse repetition

frequency (PRF), which randomizes detected RF interference while maintaining echo signal

coherence. The invention relates to short-range pulse-radar with constant false alarm rate

(CFAR) detector. The PRF generator is modulated by the noise generator. The range gate

timing relative to an echo return is not affected by the randomized PRF, the RF interference is

however randomly sampled. This results in broader spectral width of the interference signal

than the desired radar signal allowing filters to separate the receive signal into signal channel

and in interference channel with help of signal filter and interference filter. After signal and

interference envelope detector the output of both channels is given on CFAR detector. The

output of the interference provides o reference level for a CFAR threshold detector, so the

radar sensor does not give false triggers due to RF interference.

Fig. 3.1.2.1 Block diagram of a radar receiver


Restriction to a specific radar type Short-range pulse-radar with CFAR

Implementation effort Medium, implementation in hardware and processing


Mitigation effect on TX path no

Mitigation effect on RX path yes

Computational effort Medium

Interference mitigation category Time domain

Harmonization needed no

MOSARIM relevant yes

Range of mitigation effect Theoretically no false detection

3.1.3 PREF03 – Radar apparatus and radar system for a vehicle

Abstract: In this patent the inventor proposes to operate radar system for automotive with multiple

sensors on a single vehicle. The system includes interference detector which determines the

presence or absence of the interference on the basis of the received wave. Each of the radar

sensors in the system can take one of the modulation states. Modulation states differ with

carrier frequency, modulation type, orientation of polarization plane of the wave, transmission

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cycle, and/or modulation code. When the interference detector detects interference the

modulation state selector selects randomly a new modulation state for the radar sensor. The

interference can be avoided by communication of used modulation states. Communication

between radar sensors in the same vehicle can be carried out by CAN communication,

communication with other vehicles can be carried out by inter-vehicle communication or by

road-vehicle communication. Proposed is also a priority identification codes. This method

ensures that the radar sensor having the higher priority can operate without interference.


Restriction to a specific radar type no

Implementation effort High: detection of interference, various modulation stated, communication between sensors


Mitigation effect on TX path yes


Computational effort moderate

Interference mitigation category Detect and avoid (various domains)

Harmonization needed yes


Range of mitigation effect Depending on used modulation states

3.1.4 PREF04 – Automotive radar with composite multi-slope FM chirp waveform

Abstract: In this patent the inventor proposes using a multi-slope FM chirp waveform in dense-signal

multiuser environment. The slopes of the chirp signals are normalized to the mean slope and

the duration time is the same of all transmitted chirps. The slopes of the chirp signals are

optimal chosen as chirp pair with opposite slopes or four chirps with opposite as well as

inverse slopes. With chirp quadruples and chirp doublets other configuration of the transmit

signals can be constructed. A burst of chirps is transmitted where the time gap between two

bursts can vary in some regular or irregular fashion. In the burst separate chirps are selected in

a random order. Form the received radar signal the range and the velocity of the object are

estimated using all beat frequencies form all chirp signal. In practical applications low or

moderate interference level can be tolerated with some performance degradation. In case of

catastrophic interference at one of the received chirps signal an algorithm which excludes a

pair of chirps with opposite or inverse slopes. The estimation of the range and velocity of the

objects is calculated for all cases with one pair (or two pairs) excluded. With only one

catastrophic interference achieved result is a cluster with incorrect estimation and an isolated

point appearing outside the main cluster. With suitable classification the correct range and

velocity estimate can be determined.


Restriction to a specific radar type FMCW

Implementation effort Moderate




Computational effort moderate

Interference mitigation category Frequency domain and time domain


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Range of mitigation effect t.b.d.

3.1.5 PREF05 – Fourier-transform-based adaptive radio interference mitigation

Abstract: In this patent the inventor proposes an adaptive noise cancelation technique for Radio

Frequency interference (RFI) mitigation applicable in Synthetic Aperture Radar (SAR) image

processing. Proposed interference cancelation uses for the RFI rejection pre-nadir data, which

are data recorded before the radar nadir returns and post-nadir data. Assumed is the post-nadir

data are superposition of a signal which is either target or clutter and noise interference

component, and the pre-nadir data is taken as observation of the interference. An optimal

signal estimate can be obtained through subtraction of the interference estimate from the post-

nadir data. The interference estimate is calculated from pre-nadir and post-nadir data. This

approach can be used for suppression of the ‘stationary’ RFI. The FOPEN III receivers have

problems with unbalanced I- and Q-channels and timing errors. Proposed in this patent

algorithm initially removes separately the average range bias of the I- and Q-channel. Next

both channels are equalized by properly compensating their phase difference and gain

imbalance due to either constant or random timing jitter. Following the I/Q equalization,

adaptive RFI rejection is performed.


Restriction to a specific radar type SAR, pre- and post-nadir data, IQ-demodulation

Implementation effort Moderate, if pre- and post-nadir is recorded




Computational effort Moderate, rejection of the RFI in signal processing

Interference mitigation category n/a


MOSARIM relevant no

Range of mitigation effect ~20dB

3.1.6 PREF06 – Doppler Radar

Abstract: In this patent the inventor proposes to detect interference in a certain frequency range above

the system IF frequency range by using a respective band pass filter. If interference occurs,

the transmit frequency is automatically changed to avoid the interference.


Restriction to a specific radar type CW Doppler radar

Implementation effort Moderate



Mitigation effect on RX path no

Computational effort low

Interference mitigation category Detect and avoid (frequency domain)

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MOSARIM relevant yes (general approach: detect and avoid)


3.1.7 PREF07 – Frequency-phase coding device

Abstract:

In this patent the inventor proposes a Doppler-tolerant pulse-compression code generator.

Approximately orthogonal codes will prevent radar interference and suppress jamming.

Codes are generated by phase-coding the frequency-band steps and also altering the time-

sequence of the frequency steps of a step-approximation to a linear FM chirp pulse. Wide-

band radars have smaller range cells, less clutter from rain or chaff and are more difficult to

jam because of increased thermal noise power due to the wider bandwidth at the radar

receiver.

To permit many wide band radars to share the same spectral space without mutual

interference, multiple sets of uncorrelated codes are required. Unfortunately the known coding

techniques, e. g. pseudorandom phase coding, are intolerant to Doppler shift. The most

Doppler tolerant pulse coding sequence is linear FM or step approximation to linear FM pulse

coding.


Restriction to a specific radar type FM or FSK wideband radar systems

Implementation effort medium

Side-effect with other methods Nothing indicated



Computational effort medium

Interference mitigation category Coding domain

Harmonization needed t.b.d.

MOSARIM relevant probably


3.1.8 PREF08 – System and method for reducing a radar interference signal

This interference mitigation method uses the comparison of signal-slopes with threshold

values to determine, whether interference is present or not. The method was applied again for

a FMCW radar system. The principle of the complete radar system is shown in Figure

(3.1.8.1). If no interference is detected, signal (76) is directly processed by the radar return

signal processor. If interference is detected, the interference is found and removed and then

handed over to the radar return signal processor.

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Figure 3.1.8.1: Complete radar system principle

After the A/D-conversion (74), the signal is scanned for interference by the interference

detector (78). Within the interference detector, the slope is calculated by the formula

for j=1:N-1, where j is the array index that indicates a change in time with the sample time ∆t.

Thresholds for comparisons are created out of look up tables or formulas, which are based on

inside knowledge and are not described in full detail within this patent. However, the

principle of the interference detector is the following:

Figure (3.1.8.2) shows two graphs. The lower one represents the digitalized analog signal at

point (76) in Figure (3.1.8.1). Out of this digitalized signal, the interference detector (Figure

(3.1.8.1), box 78) creates the slope over time (Figure (3.1.8.2), upper graph). The interference

detector indicates interference if the slope of the received signal exceeds thresholds like 122

and 124 for a not in detailed specified number of samples (here, 122 is a threshold based on a

slope maximum, 124 is a threshold based on a mean slope value). If interference is indicated,

the zone of interference is marked. In Figure (3.1.8.2), upper graph, the zone of interference

begins at 130 and ends at 132. Now, the interference extent processor inserts so called “guard

bands”, which should help avoiding relevant discontinuities. The guard bands do not more

than extending the zone of interference by moving indices before and after the threshold

exceeding points. In the lower graph in figure (3.1.8.2), the extended zone of interference is

placed between (160a) and (160b). The last step of this interference mitigation method is done

by the interference removal processor, which zero pads the zone of interference or replaces it

by mean slope values, or something like that. The authors used zero padding and presented

their results in Figure (3.1.8.3).

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Figure 3.1.8.2: Interference detector zone

Figure 3.1.8.3: Not interfered receive signal

Signal (12) in Figure (3.1.8.3) is a not interfered receive-signal. The peak (14), caused by a

target reflection, is clearly visible at frequency f1. Signal (18) shows the same signal with

heavy interference, what avoids a high probability for indicating the target peak at f1. Signal

(212) is the result of applying the above described interference mitigation method to the

signal (18). The noise floor is indeed higher than the noise floor of signal (12) and the target

peak is a little bit wider, but the target peak is still clearly visible.

Instead of zero padding, also a weighting function could be used to suppress the interference

in the zone of interference. Also, the thresholds have not to be slope-values, they can be

derivatives of every order as well as power levels.

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General comments:

The idea to introduce thresholds dependent on derivatives is common praxis in the industry.

This method is interesting, because it is easy to apply, but still effective. The observation of

more derivatives can further increase the interference detection accuracy.


Restriction to a specific radar type FMCW, but could be adapted to others

Implementation effort Medium, because the tuning of this method will need some time.



Mitigation effect on RX path Yes, zero padding or replacement by other values

Computational effort medium

Interference mitigation category Detect and repair (time domain)

Harmonization needed No


Range of mitigation effect ~40dB (Figure 3.1.8.3), depends on kind of interference

3.1.9 PREF09 – Pulse Doppler radar interference reduction method for vehicle anti-collision or building security system

Abstract:

In this patent the inventor proposes to code the phase of the transmitted pulse at a Pulse-

Doppler-radar. At the receiving unit the received pulse will be decoded correspondingly. With

this method disturbances will be decreased significantly. This method also increases the range

for non-ambiguous determination of targets. According to the author the third advantage is

that a lot of radar sensors based on the same technology can run close by each other without

disturbing the others.

The author proposes to set the zero phases at transmitter to φ or to φ +180°. This results in a

complex pointer for phi to )(ϕji eAS ⋅= and for φ + 180° to)()180( ϕϕ jj

i eAeAS ⋅−=⋅=°+ .

According to the inventor this results in a general formula for the complex pointer

to )(ϕjii eApS ⋅⋅= , whereby pi is either +1 or -1. At the receiving stage the echo the

transmitted pulse Si has to be multiplied with -pi.

The inventor also proposes to realize this phase coding by a pseudo noise sequence to

suppress Multiple – Around – Echoes and to use different codes for several radars for

additional reduction of disturbance.


Restriction to a specific radar type Described for pulse Doppler radar

Implementation effort Small, because only the software has to be changed




Computational effort Slight higher


Harmonization needed No, different coding even improves the mitigation of interference

MOSARIM relevant yes, idea is upgradable

Range of mitigation effect ~15dB ( prevent occurrence of ghost targets, but results in increase of noise floor)

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3.1.10 PREF10 – Interference determination method and FMCW Radar using the same

This patent is very similar to patent US20060125682A1 that is also discussed in this

deliverable. Instead of talking about slopes for comparisions with thresholds, this patent talks

about variations and comparision with thresolds. The variation is the difference in voltage

between two samples in a row.

However, this interference mitigation method is also applied for an FMCW radar. The main

idea of this method is to sample the IF-signal with two times the maximum appearent beat-

frequency and compare the variation of the sampled signals with a threshold. The maximum

appearent beat-frequency is determined by the maximum range and maximum relative

velocity to be measured by the radar system. The reason why the sampling rate has to be at

least (or maybe even better equal) two times the maximum beat frequency is, that a non

interfered sinusodial IF waveform at the mixer output will always have a variation of about

the normal amplitude. If there is interference, what results in increased IF frequency

components, this variation is exceeded. Figure (3.1.10.1) shows the non interfered signal

section on the left and the interfered signal section on the right.

Figure 3.1.10.1: Non-interfered and interfered signal section

The flow chart of this interference mitigation concept is shown in Figure (3.1.10.2). The

handling is quiet similar to the other Denso patent US20060125682A1. Both use zero padding

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for eliminating the interference in radar signals. Here, this happens in (S140) of Figure

(3.1.10.2).

Figure 3.1.10.2: Flow chart of interference mitigation concept

General comment:

This patent is more an extension of Denso’s first patent. Here, the slope is abstracted to a

variation and the interference elimination itself is better described in Denso’s first patent. But

both patents US20060125682 A1 and US20070018886 A1 are interessting and can be

combined.


Restriction to a specific radar type Signal sampling radar systems

Implementation effort small


Mitigation effect on TX path Yes, carrier frequency change

Mitigation effect on RX path Yes, zero padding

Computational effort small



MOSARIM relevant yes, can maybe used in combination


3.1.11 PREF11 – Interference Avoidance System for Vehicular Radar System

A short overview of the radar system, to what the mitigation method was applied:

The reviewed patent US005280288A introduces a software-algorithm mitigation method that

can possibly by useful for different kinds of radar systems if it is adapted. In this patent, the

mitigation method is applied for a time division multiplexed radar system that successively

transmits a signal consisting of two (or more) sections with constant frequencies.

At the receiver, the difference in frequency of transmitted and received signal is created with

a mixer-device. This difference-frequency is exactly zero for a relative velocity of zero (=not

moving target). If there is a relative moving between victim and target, then the difference-

frequency is the Doppler-frequency-shift caused by the observed target. Next, the mixer-

output signal is sampled and transformed into frequency domain with an FFT. Here, the

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relative velocity and range are calculated by the equations listed in column 13 in patent

US005302956A, what is closely related to the patent US005280288A.

The interference mitigation method of patent US005280288A:

The basic principle of this interference mitigation method is to change the carrier frequency in

the case of interference. The decision, if there is interference or not, is made by the

comparison of a predetermined threshold with the receive signal’s noise level power, which is

calculated out of the receive signal’s FFT. If it is decided that interference is present (noise

level in receiver bandwidth exceeds threshold), the carrier frequency is changed. Then, again

the receive signal is checked for interference and the carrier frequency is changed again, until

there is no more interference in the receiver bandwidth, or the carrier frequency was changed

to often. In this patent, up to 4 carrier changes are allowed. The threshold itself is determined

by the averaging of calculated noise-level powers at different, random carrier frequencies, or

is simply set to values out of look up tables.

To apply the mitigation method fast and not to waste much time, there are done checks for

interference with as few samples as possible. So the system does not have to process all the

data first, only for coming to the conclusion, that there is too much interference and the results

cannot be further used. In this patent, the check for interference is done after 1024, 2048 and

4096 samples, and the calculation of the relative velocity and range are done in parallel after

1024, 2048 and 4096 samples.

Figure (3.1.11.1) shows the block diagram for the applied mitigation method. The processing

of 2048 and 4096 samples is only done, if there is no interference over a certain time.

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Figure 3.1.11.1: Block diagram of the applied mitigation method

General comment:

This method is useful for the Radar presented in the patent US005302956A, because the

Doppler resolution increases with observing-time, but the calculations can also be done with

less samples and lower Doppler resolution. This could be useful to maintain tracking, maybe.

For other kind of radars this “stepped” mitigation method could maybe adapted for a tradeoff

between interference probability and Doppler-resolution.


Restriction to a specific radar type Stepped frequency with longer constant frequencies

Implementation effort small

Side-effect with other methods Nothing expected, may be combined with others

Mitigation effect on TX path Yes, carrier change

Mitigation effect on RX path Yes, minimizing time for interference detection




MOSARIM relevant yes, can maybe used in combination


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3.1.12 PREF12 – Vehicular distance-warning radar

Abstract:

In this patent the inventor proposes to use a specific 45 degree linear polarization for both the

transmit and receive antenna of a vehicular distance warning radar. While the power reflected

from obstacles in front of the radar device is not affected by the 45 degree slant polarization

as both the transmit and receive antenna operate in the same electric field-vector plane the

interference effect from oncoming vehicles equipped with the same radar device is drastically

reduced due to the cross-polarization effect (see 2.1). The victim radar receive antenna (with

45 degree polarization) sees the polarization of the oncoming interference radar at 135 degree

that is 90 degree shifted in phase and thus results in the minimum susceptibility for

interference. The invention can be likewise used for rearward-looking radars of vehicles

driving in the same direction. For this case the rearward-looking radars shall have a 135

degree slant polarization to minimize the interference effect.


Restriction to a specific radar type No, can be used for any kind of vehicular radar

Implementation effort small, because realized in hardware by specific antenna design




Computational effort negligible

Interference mitigation category Polarization domain

Harmonization needed Yes, because polarization must be identical for all devices


Range of mitigation effect 10 dB to 30 dB

3.1.13 PREF13 – Radar system for detecting surroundings with compensation of interfering signals

Abstract:

The scope of this patent is limited to the FMCW radar principle. The basic idea is to eliminate

or reduce the effect of an interfering radar signal by applying a dithering effect to the FMCW

radar operational parameters. At least one of the following parameters is therefore changed

over time:

� The start time of the frequency slope � The delay time until the IF-signal is first sampled with the analog-to-digital converter � Time variation of the transmit and receive interval � The idle time between the up- and down- frequency slopes � The steepness of the slope and whether the up or down slope starts first � The absolute start frequency of the up- and down-slope By applying at least one of the above mentioned means the effect of an interfering signal will

be reduced in the frequency domain (after the FFT processing) by smearing its interference

power in a larger bandwidth. A significant reduction may only occur if the interference signal

is uncorrelated to the changing process of the parameters. With FM slope start time variation

By another claim of this patent interference effects are further reduced by applying non-linear

filtering and averaging over several FFT spectra.

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Fig. 3.1.13.1: Simulation of the reduction of the interference signal (2) by 18 dB with time

variation of the transmit and receive interval


Restriction to a specific radar type Only possible for FMCW radar type

Implementation effort Medium hardware effort and large processing effort for averaging over multiple FFT spectra




Computational effort Medium to large

Interference mitigation category Time and frequency domain

Harmonization needed No, parameter variation should be uncorrelated


Range of mitigation effect 20 dB

3.1.14 PREF14 – Method for the suppression of disturbances in systems for detecting objects

The scope of this patent is limited to pulse-Doppler radar principle. The pulse repetition

frequency of the Doppler radar is pseudo-noise coded to reduce interference with other radar

systems. Nevertheless interference is still possible and the interference effects manifest by

sharp peaks in the time signal. With the use of non-linear filtering (e.g. multi-stage median

filters) interference peaks can be reduced, as shown in Fig. 3.1.14.1.

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Fig. 3.1.14.1: Reduction of interference peaks in a pseudo-noise pulse-Doppler radar signal by

median filtering of the time signal


Restriction to a specific radar type Only possible for pulse-Doppler radar type

Implementation effort Medium hardware and processing effort


Mitigation effect on TX path yes, PN coding


Computational effort Medium




Range of mitigation effect 20 dB

3.1.15 PREF15 – Automotive radar system with anti-interference means

Described in this patent is a method to detect interference from other radars and a method for

finding unused frequency slots. Fig. 3.1.15.1 shows the method for detecting interference

from other radars based on the radar’s FFT spectrum (FMCW radar). Upon the detection of

interference other vehicles are queried either directly or indirectly via a base station to find an

unused frequency slot for the disturbed radar (see Fig. 3.1.15.2).

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Fig. 3.1.15.1: Detection of interference from other radars based on the radar’s FFT spectrum

(FMCW radar).

Fig. 3.1.15.2: Communication scheme: Either direct communication between vehicles or

indirect communication between vehicles via a base station


Restriction to a specific radar type FMCW radars

Implementation effort large, since communication between vehicles is required




Computational effort In the radar sensors: Limited

Interference mitigation category Detect and avoid, communicate and avoid (frequency domain)

Harmonization needed Yes, all vehicles need to be able to communicate

MOSARIM relevant Depends on whether communication between vehicles will be considered as an option

Range of mitigation effect Method to avoid interference by the use of separate frequency bands; high mitigation expected

3.1.16 PREF16 – Interference rejection method for an automotive radar CW/ICC system

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The patent describes a method for FMCW radars to detect and eliminate so-called transient

pulses which can e.g. be generated by interference from other FMCW radars. Fig. 3.1.16.1

shows such a transient pulse in the samples of the intermediate frequency signal of a FMCW

radar. The method locates the transient pulse and sets the affected samples to zero. The signal

is then interpolated to fill the gap. The reduction of the noise floor in the FFT spectrum of the

intermediate frequency signal which is achieved by the method can be seen in Fig. 3.1.16.2.

Fig. 3.1.16.1: Transient pulse in the samples of the intermediate frequency signal of a FMCW

radar

Fig. 3.1.16.2: Comparison between the disturbed FFT spectrum of the intermediate frequency

signal and the FFT spectrum obtained after applying the method.



Implementation effort low (digital signal processing of the samples before the FFT)




Computational effort Should not be too large



MOSARIM relevant Yes, since it should be relatively easy to implement this measure in existing FMCW radars

Range of mitigation effect Theoretically the interference can be completely eliminated

3.1.17 PREF17 – Procedure for the elimination of interference in a radar unit of the FMCW type

The patent describes a method to detect and eliminate so-called transient pulses which can e.g.

be generated by interference from other FMCW radars. Fig. 3.1.17.1 shows such a transient

pulse in the samples of the intermediate frequency signal of a FMCW radar. The method

locates the transient pulse and sets the affected samples to zero. The signal is then

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extrapolated from the previous samples to fill the gap. The undisturbed signal and the

extrapolated signal are compared in Fig. 3.1.17.2. It can be seen that the extrapolated signal

matches the undisturbed signal well.

Fig. 3.1.17.1: Transient pulse in the samples of the intermediate frequency signal of an

FMCW radar.

Fig.3.1.17. 2: Comparison between the extrapolated signal and the original (undisturbed)

signal.



Implementation effort low (digital signal processing of the samples before the FFT)




Computational effort Should not be too large



MOSARIM relevant Yes, since it should be relatively easy to implement this measure in existing FMCW radars

Range of mitigation effect Theoretically the interference can be completely eliminated

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3.1.18 PREF18 – FMCW Radar Device and Method for Detecting Interference

This interference mitigation method makes use of the increasing high-frequency noise floor at

the output of the receiver-mixer in the case of present interference. The interference

mitigation method is said to be effective against interference from FMCW, multiple

frequency CW, pulse and spread spectrum Radars.

A short overview of the radar system, to what the mitigation method was applied:

This patent introduces an interference mitigation method, applied for a standard FMCW

Radar device. The victim radar transmits a sinusoidal signal, swept linearly in time. This

signal is reflected by an observed target and is received by the antenna of the victim receiver-

stage. Additional, the victim receiver antenna receives some interfering signals, which are

superimposed with the use-signal. The newly formed signal is now mixed with the original

transmitted signal and the result is the IF-frequency. The IF-Frequency is now transformed

into frequency domain by an FFT.

The interference mitigation method of patent US20060181448A1:

The starting point of this mitigation method is the FFT. The FFT is divided into two sections,

a ”target detection frequency range” and a “high frequency range”, see Figure (3.1.18.1).

Figure 3.1.18.1: Two FFT sections

There are several points in Figure (3.1.18.1) that have to be remarked. The solid line

represents the FFT of the interfered IF signal, the dashed line represents the FFT of the IF

signal without interference. 123 and 124 show found targets within the detection range. Also

125 is a target, but not visible if interference is present. The zone around 126 is slightly wider

than other targets, what is caused by multipath phenomena like reflections from the side of the

road. 127 is a target outside the detection range, what is still present in this FFT. This can

only happen, if there is a very large object with a surface that stands perpendicular to the

incident radar wave.

The authors of this patent pretend that there is no synchronization between any radar system,

and the probability for an occurrence of ghosts extremely low due to non-idealities, so the

interference will only result in an increased noise floor over both frequency bands in Figure

(3.1.18.1).

Now the interference detection and mitigation works the following way:

The noise floor in the high frequency range is observed and the magnitude per frequency is

added up. The high frequency range is observed because here it is possible to sum the

magnitudes per frequency over a wider frequency span, without having very much peaks from

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targets in it. If the sum of the magnitudes exceeds a predetermined threshold, interference is

indicated. To avoid the interference (here it is called “measurement against interference”), the

carrier frequency of the radar is changed (frequency hopping), or the polarization of the

antenna is changed. Figure (3.1.18.2) shows the algorithm in a flow chart.

Figure 3.1.18.2: Flow chart of algorithm

The threshold can be determined in different ways. One possibility is to gain information

about the noise floor from other FMCW receivers at the vehicle, so there can be calculated an

interference/noise mean for the use as a threshold. Figure (3.1.18.3) shows the applied

threshold to a FFT.

Figure 3.1.18.3: Applied threshold to a FFT

General comments:

In typical FMCW radar system there is a filter after the maximum detection range that cuts off

all frequencies above Nyquist criterion. Because of that, the here introduced method will

likely be used separately on an own path after the mixer before the anti aliasing low pass (this

is mentioned in a short sentence in the patent). Then it is possible to apply a band-pass filter

to focus on the relevant frequencies for further interference detection by the microcontroller.

The important point of this detection/mitigation method is that it is applied in a higher

bandwidth region, which is less “infested” with targets and will lead to a more reliable

threshold determination.


Restriction to a specific radar type FMCW, but could be adapted to other Radars

Implementation effort low


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Mitigation effect on TX path yes, frequency change, polarization change



Interference mitigation category Detect and avoid (polarization domain, frequency domain)

Harmonization needed Yes, if polarization is switched for interference mitigation



3.1.19 PREF19 – Adding error correction and coding to a radar system

Described in this patent are the use of intra-pulse modulation to achieve a finer range

resolution and the use of inter-pulse modulation for the decoupling of different (pulsed) radars.

A pulse sequence with only intra-pulse modulation is shown in Fig. 3.1.19.1, the pulse

sequence in Fig.3.1.19.2 has both intra-pulse and inter-pulse modulation. Different radars

cannot be completely decoupled by this measure, but interference from other radars is reduced

significantly since the pseudo-noise codes used for the inter-pulse modulation have a low

cross correlation. The principle requires integration over one period of the code. Longer codes

achieve a greater mitigation factor, the trade-off is therefore between mitigation factor and

measurement duration.

Fig. 3.1.19.1: Pulse sequence with only intra-pulse modulation.

Fig. 3.1.19.2: Pulse sequence with both intra-pulse and inter-pulse modulation.

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Restriction to a specific radar type Pulsed radars

Implementation effort Requires a binary phase shift keying (BPSK) modulator




Computational effort Requires the generation of a pseudo-noise sequence (one period of a pseudo-noise code)


Harmonization needed Yes, radars need to use codes from the same set of codes

MOSARIM relevant Yes

Range of mitigation effect Depends on the code length (longer codes achieve a greater mitigation factor)

3.1.20 PREF20 – Method for operation of a radar device

The scope of this patent is limited to pulse-Doppler and FSK radar principle. A special

evaluation unit analyzes the received radar signal and determines whether an interference

signal is present or not by plausibility checks. In case the evaluation unit detects the presence

of an interferer the radar operation frequency is changed to another value that is within the

maximum allowed operational bandwidth of the radar. With this counter-measure applied a

maximum of one processing cycle can be corrupted. The radar operation frequency remains at

its new value until further interference is detected. Then either a higher or lower next

operation frequency is chosen.

The principle of operational frequency change is shown in Fig. 3.1.20.1.

Fig. 3.1.20.1: Operational frequency change of a pulse-Doppler radar that has detected the

presence of an interferer (fS = transmit frequency, fE = receive frequency, TP = pulse

repetition frequency, MZ = processing cycle, tx = interference detected)

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Restriction to a specific radar type Only possible for pulse-Doppler and FSK radar type

Implementation effort Medium hardware only




Computational effort negligible


Harmonization needed No


Range of mitigation effect very high as long as free frequencies are available

3.1.21 PREF21 – Bridge detecting and false warning suppressing method for motor vehicle, involves suppressing controller of speed controlling system changing driving conditions of vehicle, when identified objects are classified to pre-set object class

Abstract:

In this patent the inventor proposes a method to detect bridges and to suppress fail warnings

of a speed controlling system due to bridge targets.

The method involves detecting measured values concerning to a driving condition of a

moving vehicle and representing the measured values in an evaluable measured value table.

An analysis of the driving condition represented in the table is implemented, and objects are

identified using a number of criteria characterizing the objects (distance, speed, acceleration,

place of origin, life cycle of object, radar cross section). The identified objects are classified

into a set of object classes. A false warning of the speed controlling system changing the

driving conditions of the vehicle is suppressed, when the identified objects are classified to a

pre-set object class.



Implementation effort Small, just additional software algorithm

Side-effect with other methods Possible, only uninteresting static targets will be removed

Mitigation effect on TX path -


Computational effort Additional analysis algorithm necessary


Harmonization needed No, because algorithm does not influence other sensors


Range of mitigation effect Removing of uninteresting static targets

3.1.22 PREF22 – Radar device and methods for suppression of disturbance of a radar device

Abstract:

In this patent the inventor proposes a setup for a radar sensor including transmitting and

receiving path. The inventor proposes to decrease disturbance by using a code to delay the

transmitted pulse (23) and to delay reference signal (carrier) which will be mixed with the

received pulse (25). This delay should be generated by a pseudo noise code generator (13).

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According to the inventor this results in an improvement of S/N ratio. The detection of false

targets will also be decreased.

Fig. 3.1.22.1: Example architecture

The inventor also proposes to change the code cyclically to increase suppression of

disturbance.

The inventor also suggests an additional method for suppressing disturbance by the usage of

amplitude shift keying, phase shift keying and polarization of the signal.


Restriction to a specific radar type Pulse radar or radar with chirp sequences

Implementation effort Additional Software code has to be implemented

Side-effect with other methods not known



Computational effort Not negligible, additional software for coding has to be implemented


Harmonization needed no, different code for each radar sensor leads to better results between several sensors


Range of mitigation effect ~ 10dB

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3.2 Conference paper database

3.2.1 CREF01 – Reduction of Interference in Automotive Radars using Multiscale Wavelet Transform

Abstract:

A technique is presented to minimise false decisions in automotive radars operating in close

proximity. The technique also reduces the requirement on the power of the radar as signals

can be detected with very low signal to noise ratios. The signal processing is achieved in real

time using a field programmable array.

Short Explanation:

The presented Algorithm uses the Wavelet Transform to determine the position of pulse edges

(rising and falling). Only if the distance between the rising and the falling edge matches the

expected value (i.e. the width of the transmitted pulse) the received signal is accepted as a

valid reflection. In some sense the proposed technique can therefore be regarded as a form of

matched filtering.

Paper reference in Bibliography CREF01

Restriction to a specific radar type Pulsed Radars

Implementation effort medium, only signal processing needs adaption

Side-effect with other methods nothing expected, may be combined with others



Computational effort high

Interference mitigation category Detect and omit (time domain)




3.2.2 CREF02 – Reduction of Interference in Microwave Automotive Radars

Abstract:

In this document the authors proposes to implement an algorithm which reduces the

probability for false decisions and the requirement on the transmitted power. Thus, the

possibility of interference is reduced. The presented techniques depend on transmitted radar

signals with different pulse widths and different pulse repetition frequencies.

The algorithm is based on a wavelet analysis to detect the pulses which match the transmitter

own pulse width at presence of noise and false jamming signals on the received target pulse.

There are two stages for this algorithm. The Criterions for use of the first stage are a high

SNR and a low density of false jamming signals. Stage 2 is used if stage 1 fails to detect

target pulse edges. This can happen if there is a low SNR and a high density of false jamming

signals.

The algorithm also reduces the required transmitted power, because a correct detection is

possible at much lower S/N ratios. This results in a decrease of interference from

neighbouring radars.

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Patent reference in Bibliography CREF02


Implementation effort Additional algorithm

Side-effect with other methods possible



Computational effort Additional algorithm


Harmonization needed no, not needed for algorithm


Range of mitigation effect ca. 5dB

3.2.3 CREF03 – Research on Key Technologies for Collision Avoidance Automotive Radar

Abstract:

Anti-interference capability and low cost play decisive roles for the break-through on the

market of collision avoidance automotive radar. With the increasing use of automotive radar,

the mutual interference becomes an issue. This paper proposes a novel signal design and

signal processing methods for automotive radar, which combine good anti-interference

capacity and the low cost of conventional frequency modulated continuous wave (FMCW)

radar. The radar signal is easy to be generated and its signal processing can be performed by

Fast Fourier Transform (FFT) algorithm. So, the proposed new method is feasible and

effective.

Short Explanation:

The authors describe a method to minimize interference by shifting the frequency of the

transmitted signal pseudo randomly (Fig. 3.2.4). The actual frequency shift is computed via

PN-sequences. Because of this random shift in frequency the probability of the interfering

signal being mixed down into the IF- range of the victim receiver becomes much smaller. At

the same time the interference signal becomes spread in frequency by averaging over several

f

t

FMCW-Ramps

Figure 3.2.3.1: Illustration of the randomly shifted FMCW-ramps (solid) and standard

ramps (dotted)

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transmit sequences. This

Documents

Report type Deliverable Work Group WP1...MOSARIM No.248231 28.06.2010 File: MOSARIM_Deliverable_1.5_V1.6.doc 4/70 3.1.22 PREF22 – Radar device and methods for suppression of disturbance